1. Field of the Invention
The present invention relates to a slide-rotating collar which protects a rotating resin shaft, a developing device using the slide-rotating collar and an image forming apparatus using the developing apparatus, and more particularly to a slide-rotating collar with a simple construction.
2. Discussion of the Background
An image forming apparatus, in which an electrostatic latent image is formed on a surface of an image bearing member, is commonly known. The electrostatic latent image is developed into a visible image with toner by a developing device. The visible image is then transferred onto a transfer sheet to obtain a recording image.
In the above-described developing device, a conveying screw is used to stir and convey a developer. In recent years, this conveying screw has been manufactured of an integrally molded resin to reduce weight and operational load.
The conveying screw includes a rotational shaft. A bearing provided in a non-moving member supports the shaft so that the shaft rotates. The shaft rotates, for example, at a high speed of 300 rpm.
Conventionally, either a metallic pipe is inserted into a mold and molded with the shaft, or the metallic pipe is press-fitted to the resin shaft after the shaft is molded, in order to prevent wear of the resin shaft caused by a friction between the resin shaft and a metallic bearing.
However, it is difficult to form a metallic pipe having a thin wall. The thicker the wall of the metallic pipe, the smaller the diameter of the resin shaft, resulting in a decrease in mechanical strength of the shaft.
A secondary process is required to thin the wall of the metal pipe, resulting in an additional processing cost. The driving load of the shaft is increased and apparatus using the resin shaft are increased in size, when the diameter of the shaft is increased.
The present invention has been made in view of the above-mentioned and other problems and addresses the above-discussed and other problems.
The present invention advantageously provides a novel slide-rotating collar with a simple construction and at a reduced cost. The slide-rotating collar protects the rotating shaft without causing an increased driving load and without resulting in increased size of apparatus using a resin shaft.
According to an embodiment of the present invention, a collar is provided for a rotating shaft. This collar protects the rotating shaft by covering it. Preferably, the collar covers the shaft such that a contact between a bearing and the shaft is avoided, i.e. only the collar but not the shaft contacts the bearing. Preferably, the collar is constituted to allow sliding contact between the collar and the shaft for mounting the collar on the shaft. The collar is preferably made of a bent metallic plate. This metallic plate may be for instance sheet metal, a formed plate (including e.g. stamped and/or cut projections or recesses), or a planar plate. The bent shape is preferably such that it covers at least a part of the circumference of the rotating surface of the rotating shaft. Preferably the bent shape is rotationally symmetric (e.g. cylindrically or conically). Preferably the covering is such that it covers a whole circumference of a shaft, or most of the circumference of the shaft, or at least those sections where the shaft would otherwise contact a bearing. Due to a bending of the plate, two ends of the plate which were at opposite ends before bending, are adjacent to each other. There may be a distance between the two ends which is small in comparison to the circumference of the surface to be covered (e.g. smaller than 10%, preferably smaller than 1% of the circumference or the adjacent ends may contact each other). The shape of the plate is such that at least a sectional part, or a plurality of sectional parts, of the adjacent ends are inclined (at an arbitrary angle but including perpendicular) with respect to the rotational axis of the shaft, i.e. non-parallel to the rotational axis of the shaft. This inclination (preferably more than 30xc2x0) prevents a deformation of the collar during rotation of the shaft.
Preferably, the collar includes an engaging member (stopper) which allows for engagement with a mating engaging member provided on the shaft. The engaging members on the collar and on the shaft are preferably constituted such that relative rotational movement between the shaft and the collar is prevented. Alternatively or additionally, the engaging member allows fixing the position of the collar with respect to the shaft in the direction of the rotational axis. However, it is also possible to provide two different engaging members, one for fixing with respect to the rotational direction and one for fixing with respect to the axial direction. Preferably, the collar is integrally mounted on the shaft in order to avoid relative movements.
The shaft is preferably made of a non-metallic material, e.g. plastic, e.g. resin, etc. Preferably, the shaft is made of a material which has a hardness which is lower than the hardness of metal. Preferably, the collar is made of a material which has a hardness which is the same or higher than the hardness of metal. Preferably, the collar is made of metal. Preferably, the shaft is molded.